I extracted this information from Jim VanDenBerghe off of the Yahoo! MGconvert news group. In Jim's own words:

I may have mentioned this in a past post: The 2.2L Chrysler 4 cylinder engine had a bore of 87.5 mm. And all three rings are the same thickness as the Guzzi rings. So a 0.5 mm oversize ring is for a 88 mm bore - the same as the Convert. I talked to the owner of the local speed shop and he said a moly ring should work fine in a stock OEM steel cylinder or a Gilardoni cylinder. And you can get a set of 4 for about half of what a set of Guzzi rings would cost. Something to consider.